[Resolved] New Build Issues

[djencode]

Hi, I just received my kit in the mail today and assembled it. I'm encountering a few issues and was wondering what could be the situation...

1. Every time I press a button, turn an encoder, or hit a midi note, the brightness of the display alters. It bounces around from light to dark.
2. I'm hearing a high pitch noise when USB is plugged in.
3. I'm hearing RF noise when power is plugged in.

Just so you know, I'm using balanced cables (not sure if the preen's outs are balanced or not)

Edit: 4. not experiencing full polyphony. With 8 operators I'm getting between 2-8 notes depending on the patch. It's very inconsistent.

[Xavier]

Hi,

1. Seems like you have a soldering problem somewhere. Shortcut or missing point ?
You can start by follow the voltage verification in the reply #6 of this thread :
http://ixox.fr/forum/index.php?topic=63509.0

2. Can be your USB power supply. Some are very noisy. If the sound is always the same with different ones, can come from 1.

3. And not with USB ?
The preenfm2 audio is not balanced, so if your audio card expect balanced audio, the balanced cable can catch RF noise.

4. I forgot to add a little paper in the last kits i sent. On it is the URL of the manual and build instruction. In case you didn't find it :
http://ixox.fr/preenfm2/manual/synth-edit-mode/
For each of the 4 instruments, the polyphony is the number of voices you set. Set polyphony to 0 for instruments you don't use is a good best practice.

Let me know how it goes,
Best,

Xavier

[djencode]

1. I'm confused by the voltage testing. Where am I putting my multimeter leads? (not totally a n00b, but it's been centuries since I've picked up a soldering iron) From what I can deduct, this issue must be coming from power fluctuation going to the screen. How is the power being supplied to the display? That would probably help me narrow it down..

2-3. So I tried going via USB to a cube to power it straight from DC, and I got no RF noise, was just the high pitch noise I get from connecting direct to DC. That usb based RF noise is something that has been solved with balanced cables for me in the past (too bad the preen isn't balanced, is there a way to mod it to change that? Would the OLED noise reduction mod solve this problem?)

edit: i don't know if you've done away with it in this firmware but I don't hear the startup chime either...

[djencode]

Figured out the display issue, it was the OLED resistor missing haha...


now on to the noise...

it's worth noting that the high pitch from DC and the static/noise from USB don't change in amplitude from the volume button, the USB noise changes with mouse movements, and they both sit at about -81db. My Moog Sub 37 doesn't even register on the meters by comparison.

[Xavier]

Good to read you solve the OLED problem.

2.3. Can you insert a spectrum analyser (such as the free voxengo span) and let me know the frequency of the high pitch noise you hear.
If it's 15Khz, then you may want to add a shield such as explained in the oled mod thread. (No need to do the rest of the mod with PCB revision R5d if you inserted a 22R in the resistor slot called "OLED".)

When your use the USB AND a DC in power supply you have to remove the Jmp2 jumper. Is it your case ?
(removing Jmp2 prevent the USB 5V from arriving into the circuit as the DC in already provide currant).

The boot sound is a setting option, take a look at 3.1 here :
http://ixox.fr/preenfm2/manual/menu-mode/

Xavier

P.S. I don't know what images you tried to post but i cannot see them.

[djencode]

So the noise I'm hearing is at 13.3khz with an amplitude of -60db when plugged into DC with no USB. With USB and no DC it's 12.9khz with some broadband noise underneath at an amplitude of -63db. The band with DC only is very narrow whereas with USB it's a bit wider. It's actually very jarring to hear, it kinda feels like someone is constantly blowing a dog whistle lol...


The images were of my soldering job. Was trying to find a usable way to share them. May not be relevant anymore. I've ordered the metal case and the kind gent said he would also include the shield mod for free, so I'll see if that resolves the issue. Is there anything else you can think of that could help? (just in case that doesn't work?)

edit: don't let all my questions deter from the fact that this is an incredible synth!!

[lokki]

you can make a shield for yourself, see here:

http://ixox.fr/forum/index.php?topic=69159.0

i made one with 128 layers, just to be sure :-) while the noise is still there when i listen to the synth (as in put my head close to the unit and listen), it is completely gone on the audio-path. you have to adjust the position while the preenfm is running so you can see/hear when the frequency disappears.

that is just in case the metal case mod does not eliminate all the noise.

[Xavier]

I think the difference between the USB and the DC in is only because of the difference of voltage they provide.
USB is often a bit less than 4.8V.
On top of that USB often adds noise that reach the audio path...

Before trying the shield, make sure you solder a 22 ohm resistor in the "oled" resistor slot on the PCB.

XAvier

[djencode]

I think the difference between the USB and the DC in is only because of the difference of voltage they provide.
USB is often a bit less than 4.8V.
On top of that USB often adds noise that reach the audio path...

Before trying the shield, make sure you solder a 22 ohm resistor in the "oled" resistor slot on the PCB.

XAvier

Indeed I did do that. That's how I fixed my issue with the OLED changing changing brightness every time i pressed a button

[djencode]

This fixed the problem. Thanks so much! I guess that means when I get the metal shield and metal case in the mail it will solve my problem. This will work in the interim!
edit: I kinda feel like a prefabricated shield should be included as a part future kits. I know you intended the resistor to resolve the issue, and it does reduce SOME of the noise, but a shield is still required it looks like.

[Xavier]

This fixed the problem. Thanks so much! I guess that means when I get the metal shield and metal case in the mail it will solve my problem. This will work in the interim!
edit: I kinda feel like a prefabricated shield should be included as a part future kits. I know you intended the resistor to resolve the issue, and it does reduce SOME of the noise, but a shield is still required it looks like.

Good news 

The resistor alone is not suposed to fix the problem.
"Resistor + Shield" is the solution